1. IntroductionSeveral kinds of RF (radio frequency) radiated immunity/susceptibility test methodshave been proposed, and put to practical use. The test methods using trans-verse-electromagnetic (TEM) devices such as TEM cell and GTEM cell have already beenstandardized. By using these methods, the immunity/susceptibility characteristics to the elec-tromagnetic (EM) field in a fixed direction or of a constant polarization can be obtained. On theother hand, an immunity/susceptibility test method using EM field with slowly rotating polari-zation (rotating-EM field) has been proposed in reference [1]. The rotating-EM field differsfrom the circular-polarization field, that is, the polarization plane of the field rotates in a muchlower frequency than the carrier frequency. By using the rotating-EM field in the immu-nity/susceptibility measurement, the radiated immunity/susceptibility characteristics ofequipment under test (EUT) for various polarizations can be obtained easily in a short time.Moreover, by using a turntable together, the immunity/susceptibility characteristics for incidentangles of the EM field can be automatically measured at the same time. However, there are afew weak points in the system in [1]; some synchronous signal generators (SGs) is necessaryto generate the rotating-EM field accurately and the generating system is complicated.Therefore, the immunity/susceptibility measurements to various frequencies in a wide bandare difficult in the method.In this study, a new system for generating the rotating-EM field is proposed. The newgenerating system is composed of a microprocessor, some voltage-variable attenuators(VVAs), and some bi-phase switches, and only one SG is necessary for the system to gen-erate the rotating-EM field. By using this system, it is expected that the rotating-EM field of anarbitrary polarization in a wide-frequency band can be generated more easily. The principle ofthe proposing system is clarified. Moreover, the rotating-EM field is generated in an anechoicchamber and then the basic characteristics of the resultant field are examined. In addition, thePROCEEDINGS OF ISAP2005, SEOUL, KOREA- 3 -WA1-1ISBN: 89-86522-77-2 94460 KEESsusceptibility of an EUT is measured by using the new generating system, and the effective-ness of our proposed system is verified.2. Principle of new generating systemThe rotating-EM field can be generated by using two different double-side-band sup-pressed-carrier (DSB-SC) signals given byEx= sinωt cosΩt (1)Ey= sinωt sinΩt (2)where ω and Ω are angular frequencies of the carrier and field-rotating rate, respectively. TheDSB-SC signals are usually generated using a mixer in the telecommunications equipment.However, these DSB-SC signals for generating the rotating-EM field used in the proposedimmunity/susceptibility test method cannot be generated by using the mixer because the ro-tating rate of the field is less than 1 Hz, so that the unwanted components included in theDSB-SC signal generated using the mixer cannot be suppressed. These DSB-SC signals canbe rewritten in an expansion form( ) ( ){ }ttExΩ−ω+Ω+ω= sinsin21(3)( )( )⎥⎦⎤⎢⎣⎡⎭⎬⎫⎩⎨⎧π+Ω−ω+⎭⎬⎫⎩⎨⎧π−Ω+ω=2sin2sin21ttEy(4)These equations show that the DSB-SC signals are composed of four-signal components withdifferent frequencies and phases. Based on this idea, two DSB-SC signals have been gener-ated by combining four signals generated using four SGs corresponding to the above fourcomponents. In this method, unwanted-frequency components are not theoretically generatedbecause nonlinear elements are not used. Therefore, the DSB-SC signals not including anyspurious components can be generated.However, four SGs are needed in thismethod, and it is difficult to generate theDSB-SC signal of an arbitrary frequencyin a wide-frequency band easily. A newgeneration method of DSB-SC signalsproposed here is composed by a micro-processor, some attenuators, andbi-phase switches as shown in Fig. 1.The envelopes of the DSB-SC signalsexpressed by Eqs. (1) and (2) are |cosΩt|and |sinΩt|, respectively. And the phasesof these DSB-SC signals are reversedperiodically. Such time variances inthese amplitudes and phases are ad-justed with some VVAs and bi-phaseswitches, which work under the controlthrough a direct-digital synthesizer by amicroprocessor. Figure 2 shows anexample of measured waveforms of theoutput signals generated by the newDSB-SC signal generator. These wave-forms show the envelopes of two-0.04-0.0200.020.04-0.4-0.200.20.4Amplitude [V]Time [sec.]Fig. 2. Envelopes of output signals of DSB-SC signalgeneratorVoltage forswitch controlsinωtsinωt sinΩtsinωt cosΩtRF SGBi-phaseswitchBi-phaseswitchVVAVVADirect-digital synthesizerVoltage forswitch controlDividerFig. 1. Block diagram of new DSB-SC signal generator- 4 -DSB-SC signals for generating the 1-GHz EM field rotating at a frequency of 1 Hz.3. Basic characteristics of rotating-EM fieldEstimation of the basic characteristicsof the rotating-EM field generated by thenew DSB-SC signal generator has beenconducted in an anechoic chamber. Therotating-EM field generated by adual-polarized horn antenna as a transmit-ting antenna is observed at a position 4 maway from the transmitting antenna (See Fig.3). The output signals of an orthogonallyarranged dipole antenna as a receiving an-tenna were connected to a digitizing oscil-loscope through a pre amplifier, and ob-served by the oscilloscope with envelopemode. Figure 4 shows a measured wave-form of the 1-GHz-EM field rotating at a fre-quency of 1 Hz.

From the observation result,it can be confirmed that the peak of the en-velope of each output signal appears alter-nately at every 250 milliseconds. The resultsprovide evidence that the EM field rotatestwo dimensionally in a vertical plane includ-ing two elements of the orthogonal-dipoleantenna. The EM-filed uniformity in a verticalplane near the observation point was alsomeasured according to the standard speci-fied by International Electrotechnical Com-mission (IEC). From the results, we con-firmed that the EM field was satisfied with thestandard of IEC enough.4. Susceptibility measurements using newsystemThe effectiveness of the proposing testsystem was confirmed by measuring thesusceptibility of a cavity with an aperture asan EUT (See Fig. 5). The cavity is a housingmodel of a desktop personal computer, andthe internal size is a × b × c = 180 × 420 ×440 mm. The external fields couple to theinternal-EM fields of the cavity through theaperture on the wall of the cavity. Because itis experimentally confirmed beforehand thatthe cavity resonates at a frequency of 490MHz for the dominant TE011mode, it can beexpected that the cavity has high susceptibility-0.4-0.200.20.4-0.4-0.200.20.4Amplitude [V]Time [sec.]Fig. 4. Envelopes of output signals of or-thogonally-arranged dipole antenna.4 mOrthogonally arrangeddipole antennaTransmitting antenna(Dual polarized horn antenna)DSB-SCSGRF SGPre amplifier(+25 dB)Anechoic chamberDigitizingOscilloscopeTrigger source (1 Hz)Fig. 3. Observing system of rotating-EM field inanechoic chamber.Fig. 5. Structure of cavity with an aperture.b/2bcc/2aE-fieldprobeAperture- 5 -for the frequency. The susceptibility of thecavity is evaluated by measuring theoutput power of the E-field monopoleprobe arranged inside the cavity. Thecavity is set on the turntable arranged at aposition 4 m away from the transmittingantenna as shown in Fig. 6. Figure 7shows the susceptibility characteristics forthe polarization angle θ and the incidentangle φ of the EM field applied to the EUT.Here, the susceptibility is defined as anoutput power of the E-field monopoleprobe when the E-field of 1 V/m is appliedto the EUT. Figure 8 shows a comparisonof the measured results between using thenew system and the conventional systemin references [1] and [2] for θ = 90 degree.From this result, because we find the goodagreement between them, so that thevalidity of the test method using the newsystem can be confirmed.5. ConclusionThe principle of a new generationsystem of DSB-SC signal for generatingthe rotating-EM field has been shown, andthe basic characteristics have been clari-fied. Moreover, the effectiveness of theradiated immunity/susceptibility testmethod using the newly constructed sys-tem has been experimentally shown. Us-ing the proposed system could generatethe rotating-EM field modulated by varioussignals, such as analog or digital modula-tion signals. This shows that the immu-nity/susceptibility test corresponding tovarious actual electromagnetic conditionscan be conducted by using the newlyproposed system.References[1] K. Murano and Y. Kami, “A new immunity test method,” IEEE Trans. Electromagn. Compat., vol. 44, pp.119-124, Feb. 2002.[2] K. Murano, F. Xiao and Y. Kami, “An Immunity/Susceptibility Test Method Using Electromagnetic Wave ofRotating Polarization,” IEEE Trans. Instrum. Meas., vol. 53, no. 4, pp. 1184-1191, Aug. 2004.[3] Radiated, Radio-Frequency, Electromagnetic Field Immunity Test, Standard IEC 61000-4-3, 1995.-50-45-40-35-300